In an optical fiber connection, for example, in a field assembly type optical connector with a built in mechanical splice, or in a mechanical splicing unit, a method is used in which end part of a first optical fiber is butted and connected to a second optical fiber.
For the butt connection, an optical fiber connection tool is used (for example, refer to Patent Documents 1 and 2). The optical fiber connection tool comprises a support base that supporting the field assembly type optical connector in a fixed position, and an optical fiber holder that holds the optical fibers to be butted and connected. The butt connection can be performed, for example, by moving the optical fiber holder toward the field assembly type optical connector on the support base and inserting the front end parts of the optical fiber into a mechanical splice section of this optical connector.
On the other hand, as a technique for reducing the connection losses of optical fibers, there is a technique in which the front end faces of the optical fibers are beveled. If the front end faces are beveled, it is possible to reduce the reflected return light at the end faces (for example, refer to Patent Document 3).    [Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2005-134583    [Patent Document 2] Japanese Patent No. 3434668    [Patent Document 1] Japanese Unexamined Patent Application, First Publication No. H05-100117
However, in the case where optical fibers having their front end faces beveled are used, it is necessary to align the bevel directions, meaning the bevel angles and phases of the end faces of the two optical fibers accurately in order to reduce the reflected return light and have good connection characteristics. However, there is a problem in that the operation of adjusting these bevel directions is difficult.